In copending application Ser. No. 08/144,845 of even date herewith and assigned to the same Assignee as the present invention, discussion was undertaken with regard to the problems arising from the potential cross-contamination that can occur with a multi-patient fluid dispensing system. One facet of the system provided involves prevention of contamination of the multi-use segment of the fluid path during the time the system is connected to the patient. The disclosed system utilized one of two methods: a back flow preventing valve and a sterile filter, or a physical separation achieved by filling a dose container and separating the dose container from the filling fluid path before connection to the patient.
A back flow valve and a sterile filter combination should give sufficient protection. Bacteria cannot penetrate the filter. Viruses and proteins can penetrate the filter but are not active, and so cannot swim upstream. They can only diffuse. The drawbacks to this approach involve the pressure drop through the filter and volume of fluid remaining in the filter. Also, there is no way to verify that the filter is not leaking.
The present invention deals with additional methods of preventing contamination of the reusable fluid path by the patient being injected. To achieve the improved methods of preventing contamination, the present invention embodies the concept of preventing back flow, by providing no open fluid path through which bacteria can migrate or viruses or pyrogens can diffuse. (If a path is open, the velocity can then be made sufficient to prevent back diffusion.) Additionally, turbulence must be avoided since turbulence necessarily involves reverse flows and eddys that can carry material against the flow, unless the flow is high enough to prevent any part of the fluid from having a net upstream velocity vector.
Means of preventing contamination of the fluid path by contaminants other than the patient being injected are presented in copending application Ser. No. 08/144,462. Any of the concepts presented there may be matched with any of the embodiments presented here. The relevant feature is the "per patient" connection.